1. Field of the Invention
Embodiments relate to a firing method for a phase-change memory device, and more particularly, to a firing method which performs a firing operation by using a firing current in which an additional current is added to a writing current after a writing operation is performed, and a phase-change memory device.
2. Description of the Related Art
After phase-change memory cells are formed, amorphous, face centered cubic (FCC), and hexagonal closed packed (HCP) states coexist in phase-change materials included in the phase-change memory cells. The phase-change material typically exhibits a relatively low resistance in the crystalline state, which is typically defined as a “set” state or logic “0”, and a relatively high resistance in the amorphous state, which is typically defined as a “reset” state or logic “1.”
In order to improve a transition property of the phase-change materials, the phase-change materials may be in a uniform FCC state. An operation of applying high energy to realize the phase-change materials in a uniform FCC state is referred to as firing.
A firing operation may be performed by applying a firing current having high current capacity to the phase-change memory cell. Accordingly, sufficient heat may be generated on a contact interface between the phase-change materials, and thus, the phase-change materials may be arranged to be in a uniform FCC state. Thus, the phase-change materials may have a uniform resistance distribution.
In a conventional firing method, the same firing current may be applied to all phase-change memory cells. Therefore, the phase-change materials may not be arranged in a uniform FCC state using the conventional firing method.
FIGS. 1A through 1C illustrate phase-change memory cells after a preset current has been applied to the phase-change memory cells.
Referring to FIGS. 1A through 1C, after the preset firing current has been applied, a programmable volume of the phase-change memory cells (PGM) in a phase change material such as a chalcogenide alloy, e.g., a germanium-antimony tellurium (GST) alloy, may vary in accordance with a resistance size of a bottom electrode contact (BEC). FIG. 1A illustrates a phase change memory cell 100A when the preset firing current is higher than an appropriate firing current, resulting in a physical defect. FIG. 1C illustrates a phase change memory cell 100C when the preset firing current is lower than an appropriate firing current, resulting in a phase-transition not being properly performed. FIG. 1B illustrates a phase-change memory cell 100B when the preset firing current is appropriate.